Monitoring the positions of bottle caps is a challenge for the beverage industry, usually demanding intricate inspection systems. A German company has developed a system that uses just one smart camera, thus cutting costs and simplifying installation, while achieving a detection rate of almost 100%.

“Applying plastic screwcaps onto PET bottles during beverage filling involves certain difficulties which make the subsequent monitoring of the screwcap for presence and correct position very demanding,” says Bernhard Voigt, a German specialist in beverage industry installations with decades of experience.

One of the Voigt’s latest projects is an innovative idea for monitoring twist caps on PET bottles for the mineral water producer, Aqua Römer.

Variations in bottle tolerances and environmental conditions, coupled with high process speeds, are some of the main obstacles that such applications have to overcome. PET bottles can exhibit variations in height of several millimetres, especially after several washes. Any shrinkage is not necessarily symmetrical, so skewing can occur on the bottle’s neck or along the entire bottle.

Moreover, the bottle’s contents can affect to its height and width. And drops of moisture on the outside of the bottle caused by liquid sprays can make the detection of contours difficult. High production line speeds and variable conveyor conditions – from uneven belts to guide rail adjustments – can result in bottles not being aligned correctly when they pass a detector. Despite the use of fast, precise triggering systems, bottles can wobble or move. With throughputs of up to 40,000 bottles an hour, the range of these movements can be considerable.

To ensure accurate results in such applications, several detection technologies – such as X-rays, ultrasonics and image processing systems – are typically used together. Aqua Römer was using a combination of inspection systems at its large mineral water bottling plant in Baden-Württemberg, and asked Voigt to find a more economical and easier-to-use alternative. The main aim was to improve detection quality, thus reducing pseudo-scrap rates.